Soil chopping system for a dishwasher

ABSTRACT

A dishwasher with a tub at least partially defining a treating chamber, a liquid spraying system supplying a spray of liquid to the treating chamber, a liquid recirculation system defining a recirculation flow path, and a liquid filtering system. A chopping system is included to macerate foreign objects within the recirculation flow path.

BACKGROUND OF THE INVENTION

A dishwasher is a domestic appliance into which dishes and other cooking and eating wares (e.g., plates, bowls, glasses, flatware, pots, pans, bowls, etc.) are placed to be washed. The dishwasher may include a filter system to remove soils from liquid circulated onto the dishes and may include a chopper or other mechanism to macerate foreign objects entrained in the liquid.

BRIEF DESCRIPTION OF THE INVENTION

In one embodiment, a dishwasher for treating dishes according to at least one cycle of operation includes a tub at least partially defining a treating chamber, a liquid spraying system supplying a spray of liquid to the treating chamber, a liquid recirculation system including a recirculation pump having an impeller and recirculating the sprayed liquid from the treating chamber to the liquid spraying system to define a recirculation flow path, a liquid filtering system comprising a rotating filter operably coupled to the impeller such that rotation of the impeller effects the rotation of the filter, with the filter having an upstream surface and a downstream surface and located within the recirculation flow path such that the recirculation flow path passes through the filter from the upstream surface to downstream surface to effect a filtering of the sprayed liquid, and a soil chopping system comprising at least one blade mounted to the rotating filter for co-rotation therewith and defining a blade path upon rotation of the filter.

In another embodiment, a dishwasher for treating dishes according to at least one cycle of operation includes a tub at least partially defining a treating chamber, a liquid spraying system supplying a spray of liquid to the treating chamber, a liquid recirculation system recirculating the sprayed liquid from the treating chamber to the liquid spraying system to define a recirculation flow path, and a liquid filtering system including a rotating filter having an upstream surface and a downstream surface and located within the recirculation flow path such that the recirculation flow path passes through the filter from the upstream surface to downstream surface to effect a filtering of the sprayed liquid, and a first artificial boundary spaced from at least one of the upstream surface and the downstream surface such that liquid passing between the first artificial boundary and the corresponding surface applies a greater shear force on the corresponding surface than liquid in an absence of the first artificial boundary, and a soil chopping system comprising at least one blade mounted to the upstream surface of the rotating filter for co-rotation therewith and defining a blade path upon rotation of the filter.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a schematic, cross-sectional view of a dishwasher according to a first embodiment of the invention.

FIG. 2 is a schematic view of a controller of the dishwasher of FIG. 1.

FIG. 3 is a perspective view of an embodiment of a pump, filter assembly, and chopping system of the dishwasher of FIG. 1 with portions cut away for clarity.

FIG. 4 is an exploded view of the pump, filter assembly, and chopping system of FIG. 2.

FIG. 5 is a cross-sectional view of the pump, filter assembly, and chopping system of FIG. 2 taken along the line 5-5 shown in FIG. 3.

FIG. 6 is a cross-sectional elevation view of a portion of the pump, filter assembly, and chopping system of FIG. 2.

FIG. 7 is a cross-sectional view of a pump, filter assembly, and chopping system according to a second embodiment of the invention.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

In FIG. 1, an automated dishwasher 10 according to a first embodiment is illustrated. The dishwasher 10 shares many features of a conventional automated dishwasher, which will not be described in detail herein except as necessary for a complete understanding of the invention. A chassis 12 may define an interior of the dishwasher 10 and may include a frame, with or without panels mounted to the frame. An open-faced tub 14 may be provided within the chassis 12 and may at least partially define a treating chamber 16, having an open face, for washing dishes. A door assembly 18 may be movably mounted to the dishwasher 10 for movement between opened and closed positions to selectively open and close the open face of the tub 14. Thus, the door assembly provides accessibility to the treating chamber 16 for the loading and unloading of dishes or other washable items.

It should be appreciated that the door assembly 18 may be secured to the lower front edge of the chassis 12 or to the lower front edge of the tub 14 via a hinge assembly (not shown) configured to pivot the door assembly 18. When the door assembly 18 is closed, user access to the treating chamber 16 may be prevented, whereas user access to the treating chamber 16 may be permitted when the door assembly 18 is open.

Dish holders, illustrated in the form of upper and lower dish racks 26, 28, are located within the treating chamber 16 and receive dishes for washing. The upper and lower racks 26, 28 are typically mounted for slidable movement in and out of the treating chamber 16 for ease of loading and unloading. Other dish holders may be provided, such as a silverware basket. As used in this description, the term “dish(es)” is intended to be generic to any item, single or plural, that may be treated in the dishwasher 10, including, without limitation, dishes, plates, pots, bowls, pans, glassware, and silverware.

A spray system is provided for spraying liquid in the treating chamber 16 and is provided in the form of a first lower spray assembly 34, a second lower spray assembly 36, a rotating mid-level spray arm assembly 38, and/or an upper spray arm assembly 40. Upper spray arm assembly 40, mid-level spray arm assembly 38 and lower spray assembly 34 are located, respectively, above the upper rack 26, beneath the upper rack 26, and beneath the lower rack 24 and are illustrated as rotating spray arms. The second lower spray assembly 36 is illustrated as being located adjacent the lower dish rack 28 toward the rear of the treating chamber 16. The second lower spray assembly 36 is illustrated as including a vertically oriented distribution header or spray manifold 44. Such a spray manifold is set forth in detail in U.S. Pat. No. 7,594,513, issued Sep. 29, 2009, and titled “Multiple Wash Zone Dishwasher,” which is incorporated herein by reference in its entirety.

A recirculation system is provided for recirculating liquid from the treating chamber 16 to the spray system. The recirculation system may include a sump 30 and a pump assembly 31. The sump 30 collects the liquid sprayed in the treating chamber 16 and may be formed by a sloped or recessed portion of a bottom wall of the tub 14. The pump assembly 31 may include both a drain pump assembly 32 and a recirculation pump assembly 33. The drain pump assembly 32 may draw liquid from the sump 30 and pump the liquid out of the dishwasher 10 to a household drain line (not shown). The recirculation pump assembly 33 may draw liquid from the sump 30 and the liquid may be simultaneously or selectively pumped through a supply tube 42 to each of the assemblies 34, 36, 38, 40 for selective spraying. While not shown, a liquid supply system may include a water supply conduit coupled with a household water supply for supplying water to the treating chamber 16.

A heating system including a heater 46 may be located within the sump 30 for heating the liquid contained in the sump 30.

A controller 50 may also be included in the dishwasher 10, which may be operably coupled with various components of the dishwasher 10 to implement a cycle of operation. The controller 50 may be located within the door 18 as illustrated, or it may alternatively be located somewhere within the chassis 12. The controller 50 may also be operably coupled with a control panel or user interface 56 for receiving user-selected inputs and communicating information to the user. The user interface 56 may include operational controls such as dials, lights, switches, and displays enabling a user to input commands, such as a cycle of operation, to the controller 50 and receive information.

As illustrated schematically in FIG. 2, the controller 50 may be coupled with the heater 46 for heating the wash liquid during a cycle of operation, the drain pump assembly 32 for draining liquid from the treating chamber 16, and the recirculation pump assembly 33 for recirculating the wash liquid during the cycle of operation. The controller 50 may be provided with a memory 52 and a central processing unit (CPU) 54. The memory 52 may be used for storing control software that may be executed by the CPU 54 in completing a cycle of operation using the dishwasher 10 and any additional software. For example, the memory 52 may store one or more pre-programmed cycles of operation that may be selected by a user and completed by the dishwasher 10. The controller 50 may also receive input from one or more sensors 58. Non-limiting examples of sensors that may be communicably coupled with the controller 50 include a temperature sensor and turbidity sensor to determine the soil load associated with a selected grouping of dishes, such as the dishes associated with a particular area of the treating chamber.

Referring now to FIG. 3, the recirculation pump assembly 33 is shown removed from the dishwasher 10. The recirculation pump assembly 33 includes a recirculation pump 60 that is secured to a housing 62, which is shown partially cutaway for clarity. The housing 62 defines a filter chamber 64 that extends the length of the housing 62 and includes an inlet port 66, a drain outlet port 68, and a recirculation outlet port 70. The inlet port 66 is configured to be coupled to a fluid hose (not shown) extending from the sump 30. The filter chamber 64, depending on the location of the recirculation pump assembly 33, may functionally be part of the sump 30 or replace the sump 30. The drain outlet port 68 for the recirculation pump 60, which may also be considered the drain pump inlet port, may be coupled to the drain pump assembly 32 such that actuation of the drain pump assembly 32 drains the liquid and any foreign objects within the filter chamber 64. The recirculation outlet port 70 is configured to receive a fluid hose (not shown) such that the recirculation outlet port 70 may be fluidly coupled to the liquid spraying system including the assemblies 34, 36, 38, 40. The recirculation outlet port 70 is fluidly coupled to an impeller chamber 72 of the recirculation pump 60 such that when the recirculation pump 60 is operated liquid may be supplied to each of the assemblies 34, 36, 38, 40 for selective spraying. In this manner, the recirculation pump 60 includes an inlet fluidly coupled to the tub 14 and an outlet fluidly coupled to the liquid spraying system to recirculate liquid from the tub 14 to the treating chamber 16.

A liquid filtering system is illustrated as including a rotating filter 74 and a soil chopping system is illustrated as including a blade 80 mounted to the rotating filter 74 for co-rotation therewith. The blade may be formed of any suitable material including stainless steel, plastic, ceramic, or a metal alloy. The blade 80 may define a blade path 82, schematically illustrated with arrows, upon rotation of the rotating filter 74. While only a single blade 80 has been illustrated it is contemplated that multiple blades may be included in a manner such that they form the same blade path 82 with rotation of the rotating filter 74.

FIG. 4 more clearly illustrates that the recirculation pump assembly 33 may include a recirculation pump 60 having a motor 61 and an impeller 63, which may be rotatably driven by the motor 61. A shroud 84, the rotating filter 74, an internal flow diverter 86, a bearing 88, a shaft 90, and a separator ring 92 may be included in the recirculation pump assembly 33. The general details of such a recirculation pump assembly 33, rotating filter 74, shroud 84, and internal flow diverter 86 are described in the commonly-owned patent application entitled, Rotating Filter for a Dishwashing Machine, filed Jun. 20, 2011, and assigned U.S. application Ser. No. 13/163,945, which is incorporated by reference herein. It is contemplated that the soil chopping system having the at least one blade 80 may be used with any type of recirculation pump assembly having a rotating filter and that the recirculation pump assembly, rotating filter 74, shroud 84, and internal flow divert 86 described herein are merely for exemplary purposes and to provide the necessary details for implementing the illustrated embodiment.

The rotating filter 74 may be located within the recirculation flow path and may be operably coupled to the impeller 63 such that rotation of the impeller 63 effects the rotation of the rotating filter 74. The rotating filter 74 may include a filter sheet 75 having perforations to allow liquid to go from an upstream surface 76 to a downstream surface 78 to effect a filtering of the sprayed liquid in the recirculation flow path. The rotating filter 74 may also include a non-perforated portion 94. The non-perforated portion 94 may encircle the rotating filter 74 and may act as a strengthening rib. The non-perforated portion 94 may be for any given surface area and may provide the rotating filter 74 with greater strength, especially hoop strength. It is also contemplated that the perforations of the filter sheet 75 may be arranged to leave non-perforated bands encircling the filter sheet 75 with the non-perforated bands functioning as strengthening ribs. In the illustrated embodiment the blade 80 is mounted to the non-perforated portion 94. Alternatively, the blade 80 may be mounted to a perforated portion of the filter sheet 75. The blade 80 may be mounted to the rotating filter 74 in any suitable manner.

Regardless of whether the blade 80 is mounted to a perforated or non-perforated portion, the blade 80 may project outwardly from the rotating filter 74 such that it extends radially from the upstream surface 76. A leading edge 96 of the blade 80 may be oriented with respect to the rotating filter 74 at a variety of angles resulting in different maceration action of foreign objects in the blade path 82. More specifically, the blade 80 may be angled such that it is more tangent to the rotating filter 74 resulting in a greater slicing action than if the blade 80 were angled more perpendicular to the rotating filter 74, which would result in more of a chopping action for the expected flow direction. The angle of the leading edge 96 of the blade 80 may also be at any angle between perpendicular and tangent to the upstream surface 76 to allow for some variation of both the slicing and chopping actions. The leading edge 96 may be oriented such that impact forces that could damage the blade 80 and/or the rotating filter 74 or cause the rotating filter 74 to get jammed may be reduced.

It will be understood that the shroud 84 forms an artificial boundary and that no portion of the shroud 84 lies within the blade path 82. In the illustrated example, the shroud 84 includes a slot 98 through at least a portion of the shroud 84. More specifically, the slot 98 runs through a circumferential portion of the shroud 84. In the illustrated embodiment, the shroud 84 defines an interior 100 (FIG. 5), within which the rotating filter 74 may be located and which is fluidly accessible through multiple inlet openings 102. It is contemplated that the shroud 84 may include any number of inlet openings 102 including a singular inlet opening. As the spacing of the shroud 84 relative to the filter 74 varies radially, and is at some locations greater than the height of the blade 80, it is not necessary for the slot 98 to extend completely around the shroud. Instead, the slot 98 is located only at the positions where the blade 80 would otherwise contact the shroud 84.

When assembled, the bearing 88 may be mounted in an end of the rotating filter 74 and may rotatably receive the stationary shaft 90, which in turn may be mounted to an end of the stationary shroud 84. In this way, the rotating filter 74 may be rotatably mounted to the stationary shaft 90 with the bearing 88. The internal flow diverter 86 may also be mounted on the stationary shaft 90. The stationary shroud 84 may be mounted at its other end to the separator ring 92, which in turn is attached to the recirculation pump 60. Thus, the shroud 84 and internal flow diverter 86 are stationary while the rotating filter 74 and its attached blade 80 are free to rotate about the stationary shaft 90 in response to rotation of the impeller 63. The filter chamber 64 envelopes the shroud 84, the rotating filter 74, and the chopping system with the blade 80.

In operation, wash liquid, such as water and/or treating chemistry (i.e., water and/or detergents, enzymes, surfactants, and other cleaning or conditioning chemistry), enters the tub 14 and flows into the sump 30 to the inlet port 66 where the liquid may enter the filter chamber 64. As the filter chamber 64 fills, liquid passes through the perforations in the rotating filter 74. After the filter chamber 64 is completely filled and the sump 30 is partially filled with liquid, the dishwasher 10 activates the motor 61. During an operation cycle, a mixture of liquid and foreign objects such as soil particles may advance from the sump 30 into the filter chamber 64 to fill the filter chamber 64.

Activation of the motor 61 causes the impeller 63, the rotating filter 74, and the blade 80 to rotate. The liquid in the recirculation flow path flows into the filter chamber 64 from the inlet port 66. The rotation of the filter 74 causes the liquid and soils therein to rotate in the same direction within the filter chamber 64. The recirculation flow path may circumscribe at least a portion of the shroud 84 and enters through inlet openings 102 therein. The rotation of the impeller 63 draws liquid from the filter chamber 64 and forces the liquid by rotation of the impeller 63 outward such that it is advanced out of the impeller chamber 72 through the recirculation outlet port 70 to the assemblies 34, 36, 38, 40 for selective spraying. When liquid is delivered to the assemblies 34, 36, 38, 40, it is expelled from the assemblies 34, 36, 38, 40 onto any dishes positioned in the treating chamber 16. Liquid removes soil particles located on the dishes, and the mixture of liquid and soil particles falls onto the bottom wall of the tub 14. The sloped configuration of the bottom wall of the tub 14 directs that mixture into the sump 30. The recirculation pump 60 is fluidly coupled downstream of the downstream surface 78 of the rotating filter 74 and if the recirculation pump 60 is shut off then any liquid and soils within the filter chamber will settle in the filter chamber 64 where the liquid and any soils may be subsequently drained by the drain pump assembly 32.

FIG. 6 illustrates more clearly the shroud 84, the internal flow diverter 86, the flow of the liquid along the recirculation flow path, and the movement of the blade 80. Multiple arrows 104 illustrate the travel of liquid along the recirculation flow path as it passes through the rotating filter 74 from the upstream surface 76 to the downstream surface 78. Several of the zones created in the filter chamber 64 during operation have also been illustrated and include: a first shear force zone 106 and a second shear force zone 108. These zones impact the travel of the liquid along the liquid recirculation flow path as described in detail in the U.S. Pat. No. 7,594,513. It will be understood that the shroud 84 forms a first artificial boundary spaced from the upstream surface 76 of the rotating filter 74 such that liquid passing between the shroud 84 and the upstream surface 76 applies a greater shear force on the upstream surface 76 than liquid in an absence of the shroud 84 and that in this manner the first shear force zone 106 is formed. Similarly the internal flow diverter 86 forms a second artificial boundary spaced from the downstream surface 78 of the rotating filter 74 and creates the second shear force zone 108. The first and second shear force zones 106 and 108 aid in removing foreign soil from the rotating filter 74. Additional zones may be formed by the shroud 84 and the internal flow diverter 86 as described in detail in the U.S. Pat. No. 7,594,513.

As illustrated, the rotating filter 74 is cylindrical and as such the blade path 82 formed by the blade 80 upon rotation of the rotating filter 74 is circular. When the blade 80 is rotated, the blade 80 may act to macerate any foreign objects within the filter chamber 64 that it comes into contact with. As illustrated, the distance between the shroud 84 and the upstream surface 76 may vary; the presence of the slot 98 allows for free rotation of the blade 80 where the shroud 84 is closer to the upstream surface 76. More specifically, the slot 98 is located in the narrower portions of the shroud 84 to allow for clearance of the blade 80 as it rotates through these narrow portions and will not contact the shroud 84. It will be understood that at some points, the blade 80 may extend through the slot 98 and be capable of macerating foreign objects both inside and outside the shroud 84. As the blade 80 moves along the blade path 82 it may travel through the slot 98 and as the spacing between the shroud 84 and the rotating filter 74 increases the blade 80 may move along the blade path 82 entirely within the interior 100 of the shroud 84. The spacing between the blade 80 and the shroud 84 are such that the spacing allows the blade 80 to adequately chop or macerate foreign objects without having foreign objects become trapped between the blade 80 and the shroud 84.

FIG. 7 illustrates a recirculation pump assembly 233, which includes a chopping system according to a second embodiment of the invention. The second embodiment is similar to the first embodiment; therefore, like parts will be identified with like numerals increased by 200, with it being understood that the description of the like parts of the first embodiment applies to the second embodiment, unless otherwise noted. The chopping system in the second embodiment includes multiple blades 280. Two of the multiple blades 280 are oriented with each other such that they may form a single blade path while a third of the multiple blades 280 are oriented to form an additional blade path such that multiple blade paths (not shown) are formed upon rotation of the rotating filter 274.

Another difference is that the rotating filter 274 has been illustrated as including a first filter element 310 forming the upstream surface 276 and a second filter element 312 forming the downstream surface 278 and the multiple blades 280 are mounted to the first filter element 310 and extend outwardly therefrom. The first filter element 310 and the second filter element 312 may be affixed to each other or may be spaced apart from each other by a gap. By way of non-limiting example, the first filter element 310 has been illustrated as a cylinder and the second filter element 312 has been illustrated as a cylinder received within the first filter element 310. The first filter element 310 and second filter element 312 may be structurally different from each other, may be made of different materials, and may have different properties attributable to them. For example, the first filter element 310 may be a courser filter than the second filter element 312. Both the first and second filter elements 310, 312 may be perforated and the perforations of the first filter element 310 may be different from the perforations of the second filter element 312, with the size of the perforations providing the difference in filtering. It is contemplated that the first filter element 310 may be more resistant to foreign object damage than the second filter element 312. The resistance to foreign object damage may be provided in a variety of different ways. The first filter element 310 may be made from a different or stronger material than the second filter element 312. The first filter element 310 may be made from the same material as the second filter element 312, but having a greater thickness. The distribution of the perforations may also contribute to the first filter element 310 being stronger. The perforations of the first filter element 310 may leave a more non-perforated area for a given surface area than the second filter element 312, which may provide the first filter element 310 with greater strength, especially hoop strength. It is also contemplated that the perforations of the first filter element 310 may be arranged to leave non-perforated bands encircling the first filter element 310, with the non-perforated bands functioning as strengthening ribs.

It will be understood that any features of the above described embodiments may be combined in any manner. Further, while a specific example of a shroud and internal flow diverter have been shown and described, any suitable artificial boundaries may be used with the chopping systems described in the above embodiments. Alternatively, no artificial boundaries may be included. It is also contemplate d that the height and shape of the blades may be changed such that they will not interfere with any such artificial boundaries. Slots may be shaped to allow for the location and rotation of the blades or the artificial boundaries themselves may be configured such that no slots are necessary. For example, the contour of the artificial boundary or shroud may be such that the blade path would not interfere with the artificial boundary.

The embodiments described above provide for a variety of benefits including that the blades may create a slicing or chopping action that may reduce the occurrence of foreign objects that may damage the rotating filter or pump assemblies. Further, the embodiments described above allow for enhanced filtration such that soil is filtered from the liquid and not re-deposited on dishes and allow for cleaning of the rotating filter throughout the life of the dishwasher and this maximizes the performance of the dishwasher. Thus, such embodiments require less user maintenance than required by typical dishwashers.

While the invention has been specifically described in connection with certain specific embodiments thereof, it is to be understood that this is by way of illustration and not of limitation. Reasonable variation and modification are possible within the scope of the forgoing disclosure and drawings without departing from the spirit of the invention which is defined in the appended claims. 

What is claimed is:
 1. A dishwasher for treating dishes according to at least one cycle of operation, comprising: a tub at least partially defining a treating chamber; a liquid spraying system supplying a spray of liquid to the treating chamber; a liquid recirculation system including a recirculation pump having an impeller and recirculating the sprayed liquid from the treating chamber to the liquid spraying system to define a recirculation flow path; a liquid filtering system comprising a rotating filter operably coupled to the impeller such that rotation of the impeller effects the rotation of the filter, with the filter having an upstream surface and a downstream surface and located within the recirculation flow path such that the recirculation flow path passes through the filter from the upstream surface to downstream surface to effect a filtering of the sprayed liquid; and a soil chopping system comprising at least one blade mounted to the rotating filter for co-rotation therewith and defining a blade path upon rotation of the filter.
 2. The dishwasher of claim 1 wherein the rotating filter is cylindrical and the blade path formed upon rotation is circular.
 3. The dishwasher of claim 1 wherein the rotating filter includes at least one non-perforated portion and the at least one blade is mounted to the non-perforated portion.
 4. The dishwasher of claim 3 wherein the non-perforated portion encircles the rotating filter and forms a strengthening rib.
 5. The dishwasher of claim 1 wherein the at least one blade projects outwardly from the upstream surface of the rotating filter.
 6. The dishwasher of claim 5, further comprising a first artificial boundary spaced from the upstream surface of the rotating filter such that liquid passing between the first artificial boundary and the upstream surface applies a greater shear force on the upstream surface than liquid in an absence of the first artificial boundary and wherein no portion of the artificial boundary lies within the blade path.
 7. The dishwasher of claim 6, wherein the first artificial boundary is a shroud defining an interior and having a slot through at least a portion of the shroud so that no portion of the artificial boundary lies within the blade path.
 8. The dishwasher of claim 6, further comprising a second artificial boundary spaced from the downstream surface of the rotating filter such that liquid passing between the second artificial boundary and the downstream surface applies a greater shear force on the downstream surface than liquid in an absence of the second artificial boundary.
 9. The dishwasher of claim 1 wherein the rotating filter comprises a first filter element forming the upstream surface and a second filter element forming the downstream surface and the blade is mounted to the first filter element.
 10. The dishwasher of claim 1 wherein the at least one blade is a blade having a leading edge that is tangential to the upstream surface of the filter.
 11. The dishwasher of claim 1 wherein the at least one blade includes multiple blades.
 12. The dishwasher of claim 11 wherein the multiple blades form a single blade path.
 13. A dishwasher for treating dishes according to at least one cycle of operation, comprising: a tub at least partially defining a treating chamber; a liquid spraying system supplying a spray of liquid to the treating chamber; a liquid recirculation system recirculating the sprayed liquid from the treating chamber to the liquid spraying system to define a recirculation flow path; and a liquid filtering system comprising: a rotating filter having an upstream surface and a downstream surface and located within the recirculation flow path such that the recirculation flow path passes through the filter from the upstream surface to downstream surface to effect a filtering of the sprayed liquid; and a first artificial boundary spaced from at least one of the upstream surface and the downstream surface such that liquid passing between the first artificial boundary and the corresponding surface applies a greater shear force on the corresponding surface than liquid in an absence of the first artificial boundary; and a soil chopping system comprising at least one blade mounted to the upstream surface of the rotating filter for co-rotation therewith and defining a blade path upon rotation of the filter.
 14. The dishwasher of claim 13 wherein the first artificial boundary is spaced from the upstream surface and no portion of the artificial boundary lies within the blade path.
 15. The dishwasher of claim 14 wherein the first artificial boundary is a shroud defining an interior and spaced having a slot through at least a portion of the shroud so that no portion of the artificial boundary lies within the blade path.
 16. The dishwasher of claim 15, further comprising a second artificial boundary located adjacent a portion of the downstream surface such that liquid passing between the second artificial boundary and the downstream surface applies a greater shear force on the downstream surface than liquid in an absence of the second artificial boundary.
 17. The dishwasher of claim 13 wherein the rotating filter is cylindrical and the blade path formed upon rotation is circular.
 18. The dishwasher of claim 13 wherein the rotating filter includes at least one non-perforated portion and the at least one blade is mounted to the non-perforated portion.
 19. The dishwasher of claim 18 wherein the non-perforated portion encircles the rotating filter and forms a strengthening rib.
 20. The dishwasher of claim 13 wherein the at least one blade extends radially from an upstream surface of the rotating filter.
 21. The dishwasher of claim 13 wherein the at least one blade is a blade having a leading edge that is tangential to the upstream surface of the filter.
 22. The dishwasher of claim 13 wherein the at least one blade includes multiple blades.
 23. The dishwasher of claim 22 where the multiple blades form a single blade path. 